Apparatus for showing compass deviation



A (No Model.)

J. A. ARVIDSON. A APPARATUS FOR SHOWING COMPASS DEVIATION. No. 588,889.

.Patented May 7.1895.

UNITED *STATES j PATENT Fries,

e IOHN A. ARVIDSON, OF SANY FRANCISCO, CALIFORNIA.

APPARATUS FOR SHOWING COMPASS DEVIATION.

SPECIFICATION forming part of Letters Patent No. 538,889, dated May 7, 1 895. Application tiled November 23, 1894. Serial No. 529,766. (No model.)

' citizen of the United States, residing inthe city and county of San Francisco, State of California, have invented an Improvement in Apparatus for Showing CompassDeviation;

and I hereby declare the following tobeia full, clear, and exact description ot'A t'hesamef My invention relates to an apparatus 'which' is designed to show the deviation' of magnetic com passes, and is especially'applicable for the 'adjustment of such deviation, so that the courses sailed by the ship can be accurately determined at all times, when heavenly bodies are visible. p

It consists incertain details of construction which will bemore fully explained Vby reference to theaccornpanying drawings, in Which 'H Figure l is a view of' my apparatus. Fig. 2 is a view of the'additional segment to the compass-card. Fig. 3 is adetail 4view of the observing-tube.

A is acircularcomp'ass card supported upon gimbals in the usual way,faud having a counterbalance Weightl by which it is retained' in an essentially horizontal position lindependent of the movements of the Vessel, unles'sthe latter be very Violent. To the same support are fixed the standards B, and in these standards a circular ring C is journaled by means of pivot pins D projecting from opposite sides. This ring has marked upon it scales showing the'a'pparent time, during the whole twentyfour'hours of tlieday, and within it is fitted a disk E which is adapted to rotate within the ring. This disk is slotted across the center and has an observing tube F pivoted in the center as shown at G so as to be capable of movementabout its pivot pins to be raised or depressed with relation to the plane of the disk. In exact line with the center of this observing tube are points or indicators H which project so as to coincide with any one of the time marks shown on the inner periphery of the circle. This observing tube has cross lines or wires, as shown at-I, at one end, and the other end has an open slot made in it as shown at J. The end or bottom which is'observable through this slot has cross lines K made u pon it coinciding with the cross wiresI at the opposite open end of the tube, so

that when the tube is set in the proper direction, thelightof the sun fallingthrough it, will cause the shadow of the cross lines I to fall upon those shown at K and coincide with them. The time ring C has fixed to it a semicircular arc M. This semi-'circular arc is fixed to the time ring so as to extend below it and at right angles with the pivot pins D. Upon the inner periphery ot this arc is marked a scale lof degrees which indicates the declination, and upon its outer periphery a scale of degrees indicating latitude. At acentral point beneath this segment are a clamp N by which it maybe locked at any desired position, and astationary index or point, which shows upon the'exterior" scale the number kof degrees at which it may be set. f

The operation of the apparatus will then be as follows: `When it is desired to take an observation for the purpose of ascertaining the deviation of lthe compass, the latitude and the declination at that point being'known, the inner disk carrying the telescope or observation tube is tlrst turned so that thetube is in lineA with the latitude and declination segment. By means of an index pointerO upon the endof the tube, the declination at that particular point being known, the tube is turned upon its pivots until the indexV coincides with the marking for that declination. The outer circle C is then turned about its pivot points upon the standards until the degree indicating the latitude of that particular point coincides with the index pointer below the circle when the clamping screw is turned and the semi-circle is locked at that point` The inner disk is nowturned around Within the circle C until the index pointer, in line with the observation tube, stands opposite the ligure indicating the time at that in stant, and the apparatus is then turned or set so thatthe sun shining into the open end of the tube will throw the shadow ofthe cross hairs or wires at that end of the tube upon the corresponding cross made on the inner opposite end of the tube which can be seen through the opening J which is made at that point. When these cross wires or lines intersect, the points Q of the compass familiarly called the lubber points, will show the true meridional heading of the ship. The true va- IGO purpose and upon charts, and having this, the lubber points are adjusted to the variation, and the dierence between the heading shown by the standard compass, and that shown by the compass of this apparatus, Will be the deviation, as shown in Fig. 2. The difference between this and the standard compass will be the deviation on that course as long as that course is continued. Whenever a new course is taken the adjustment may be made again for time, the latitude and declination being approximately the same tor several observations, and the observation and correction made for the new Course.

IE a master leaving port upon a new vessel, or one in which the deviation of the compass is not known, desires to ascertain this deviation, it may be done with this-instrumentby putting the vessel successively upon various courses around the entire circle, and noting the deviation for each course. By makingan observation hole throughthe center of the end having the cross lines K, a direct observation may be made upon a star or other heavenly body not large enough to make a shadow of the cross wires, and the necessary data can thus be obtained.

This instrument may also be used to obtain the true bearing of distant points, by fixing sights R upon the observation tube, and the bearing Can be noted by the scale of degrees upon the outer periphery of the ring C when the latter has been turned to bring the tube in the proper line.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is

1. An apparatus for showing deviation of Compasses consisting of a time circle journaled in standards which are supported and turnable in conjunction with a compass, suspending mechanism whereby the compass card is maintained in an essentially horizontal position, a latitude and declination circle fixed to the lower side of the ring at right angles with its journals with an index and Clamp for adL justing and holding it, a disk rotatable within the time ring having an opening made transversely across it, an observation tube journaled in the opening in the rotatable disk so as to turn transversely thereto, and an index point in the plane of movement of the observation tube adapted to coincide with the apparent time when the observation is taken.

2. An apparatus to show the deviation of Compasses consisting of a compass card suspended and counterbalanced so as to maintain an approximately horizontal position, standards supported therefrom, an annular ring having marked upon its periphery the times from noon to midnight, and midnight to noon, a disk having a Corresponding axis and rotatable within the ring, an observation tube pivoted in a channel made transversely across the disk and turnable about its pivots with relation to the plane of the disk, cross wires fixed in the open end of the tube and a corresponding cross marked upon the inner side of the opposite closed end, with openings through which it may be seen, an index fixed to the disk adapted to coincide with the time of observation as marked upon the time ring, a semi'crcular arc fixed to the lower side of the time ring and at right angles with its axis of rotation, having the degrees of latitude marked upon its outer periphery, and a ixed index and clamp centrally beneath it whereby it may be adjusted and held, and degrees of declination marked upon its inner periphery, an index pointer fixed to the observation tube adapted to be adjusted with relation to the declination circle for the latitude in which the observation is laken.

3. An apparatus for showing the deviation of Compasses at sea, Consisting ot' a tube open at one end which is presented toward the sun or other solar object, and having crossed wires therein, a table upon the inner side of the opposite closed end having a corresponding cross marked thereon with which the shadow of the wires will coincide when the tube is properly set for the observation, and openings upon cach side ot' this end of the tube through which the coincidence of the cross lines may be observed, a disk rotatable within a ring, which ring has marked upon it theapparent times for the twenty-four hours, and an index pointer by which the disk may be setto correspond with the time when the observation is to be taken, j ournal-pins in a slotted opening extending from side to side of the disk, upon which journal pins the tube is turnable within the slot, a declination ring having degrees marked upon its inner periphery, and an index pointer upon the tube adapted to coincide with the markings of the declination ring whereby the tube may be set to the known declination in a given latitude, and degrees upon the outer periphery of the semi-circle adapted to coincide with a Central point fixed below the center of the apparatus, and a Clamp by which it is held when the ad j ustment has been made, in combination with a Compass card upon which the apparatus is supported, said card being maintained in an approximately horizontal position by gimbals and a counterbalance weight.

In witness whereof I have hereunto set my hand.

JOHN A. ARVIDSON.

Witnesses:

S. H. NoURsE, H. F. AsoHEoK.

ICO

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